The overall objective of the total project is to test if fluroide and selenium interact in dental tissues. This is designed to provide a basis for the cariogenic nature of selenium. Current studies have been directed towards measuring if different dose levels: 50, 100 and 150 microns Se/day, I.P., alter the uptake of simultaneously injected fluoride into the calcifying region of the rat incisor. No effect has been found, leading to the tentative conclusion that selenium may be caries-promoting without influencing the uptake of fluoride into enamel.